From: Gunther.Kern@astrazeneca.com
  To  : rasmb@alpha.bbri.org
  Date: Fri, 3 Aug 2001 23:28:47 +0200 

wiggles in dc/dt plots

 <<10ug_ml BSA.bmp>>  <<Wiggles in AUZ VEL.bmp>> 

I would be interested if anyone could comment on the wiggles I observe
regularily when I use DCDT to analyze velocity runs. They are tolerable if
the protein concentration is high enough as in the example I have included
in my mail. However it totally renders the option to run at low protein
concentrations since a wiggle can not be separated from what might be a
signal. Quite a shame since DCDT to my experience on other machines allows
analysis down to protein concentrations of 10 micrograms/mL. Here a few
comments on how the experiment was run. It is a monomeric protein with a MW
of 45 Kda dialysed extensively against 100mM Tris, 1 mM TCEP and 50 mM NaCl
pH8. I also know from dynamic light scattering that the sample has a few
percent of nonspecific aggregates which give the signal at around 6S. The
speed was 50Krpm at 25 dgrees. Data collection was set up to collect
interference data as fast as possible. The graph shows the overlay created
by using 20 adjacent scans. Unfortunatelly I can not release the name of the
protein but it is not a specific property of the protein. I do observe the
same when using BSA (first bitmap).
Any comment how to avaiod this problem would be very well appreciated. 

Thank you very much,

Gunther Kern
AZ R&D Boston
Infection
+781- 839 4611
gunther.kern@astrazeneca.com